1. Field of the Invention
The present invention relates to a conveying apparatus for conveying a lead frame for bonding IC chips to a bonding position thereon and, more specifically, to an improvement in the lead frame conveying apparatus.
2. Description of the Background Art
FIG. 1 is a plan view of a lead frame LF. The lead frame LF comprises an outer lead portion 111, an inner lead portion 112 on which IC chips are bonded and perforations P for conveying the lead frame to the bonding position. Conventionally, the lead frame was conveyed to the bonding position by movement of pins inserted in the perforations P. In the prior art, the size of the perforation P is larger than the diameter of the pin so as to allow insertion of the pin therethrough.
The pin must be always in contact with the edge of the hole of the perforation P in order to enable precise positioning of the inner lead portion 112 of the lead frame LF at a prescribed position to permit the same to be accurately bonded to an integrated circuit, and to maintain the lead frame exactly at the position required.
For this purpose, conventionally, lead frames assembled in continuous longitudinal strips were wound around a feeding reel, as shown in FIG. 1, and the feeding reel was energized in a direction opposed to the feeding direction of the lead frames. Consequently, a back tension was applied on the lead frame, enabling the pin to be in firm contact with the edge of the perforation P in a reliable manner.
When the lead frames are too short to be wound around the feeding reel, V shaped notches (not shown) are formed at end portions on opposite sides of the lead frame. After the lead frame fed to the bonding position is stopped at the prescribed position, V shaped projecting member for positioning engage V shaped notches P of the lead frame from above. Consequently, the inner lead portion is located at the prescribed position for bonding.
However, the above described method of conveying and positioning lead frames are practical only when the lead frame is relatively thick (for example in thickness of no less than 150 .mu.m) and is impractical when the lead frame is thin (for example, when its thickness is 50 to 100 .mu.m). The reason for this is that the tensile strength and the compressive strength of the lead frame are lost when the lead frame is thin, and there will be cracks extending from the edge of the perforation P in the lead frame. Consequently, the precise positioning of the inner lead portion at the prescribed position for bonding becomes impossible and the lead frames would not be properly positioned for bonding.